Transmission-controlling apparatus



Feb, 113, 1923.

1,444,830 C. S. DEMAREsT' TRANSMISSION CONTROLLING APPARATUS Filed Aug. 9, 19%9 3 sheets-sheet l E "S 7b flpermig Map/wile .S'et jllaizitariiy Y ATTORNEY- Feb. 13, 1923. Y i 1,444,830

1 c. s. DEMAREST TRANSMl S S ION CONTROLLING APPARATUS Filed Aug. 9, 191 9 5 sheets-sheet 2 w v m "5 F I 1 III-{r6 P E w L p i INVENTOR Wig ATTORNEY Feb, E3, 11-923 1,444,830

C. S. DEMAREST TRANSMISSION CONTROLLING APPARATUS Filed Aug. 9, 1919 5 sheets-she'et '5 To flperamn's Ylepfiane Set IN VEN TOR.

W; Y ATTORNEY Patented Feb. 13, R923.

UNETEU STA it" CHARLES S. DEMAREST, OF BROOKLYN, NEW YORK, ASSIGNOR TO AMERICAN TELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION OI! NEW YORK.

TRANSMISSION-CONTROLLING APPARATUS.

Application filed August 9, 1919. serial No. 816,416.

T 0 all whom it may concern: Y Be it known that I, CHARLES S. DEMAREST, residing at Brooklyn, in the county of Kings and State of New York, have invented certain' Improvements in Transmission-Controlling Apparatus, of which the following is a specification! This invention relates to transmission controlling apparatus and more particularly to means for controlling the operation of fourwire repeater circuits.

In the operation of four-wire repeater circuits having arepeater element in each of its two sides, kit is well known that the repeater elements may be adjusted so as to produce varying degrees of amplification of the input current or voltage wave. Such repeaters may be adjusted to produce an amplification of such magnitude that the output current at one end of the four-wire circuit is equal to the input current at the other end of the said circuit. or they may be adjusted So that the output current at one end of the circuit is greater than the input at the other end of the circuit, in which case the circuit is said .to have a. transmission equivalent better than Zero between terminals. The latter condition is sometimes desirable when it. is intended to connect twowire telephone trunk circuits with each end of the. four-wire repeater circuit. By doing this part of the losses due to the trunk circuits may be overcome.

In the operation of four-wire repeater circuits having transmission equivalent better than zero between terminals, a difficulty known as singing arises when the line circuit connected with the four-wire circuit is not balanced by the balancing network associated with the four-wire circuit. Such an unbalanced condition may arise, for example, when the operator at each end of the four-wire circuit has inserted a plug of a toll cord in the terminal jack of the fourwire circuit and has operated the listening key of the cord circuit preparatory to completing a through connection. When such av situation exists, if an electricaldisturbance reaches the repeater circuit over the cord circuit connected thereto, which does not balance the network, part of the energy flows around a circuit knownas the singing path comprising the two repeater elements and the twotriple-winding transformers, which efi'ect the relation between the two sides of the four-wire circuit. If the repeater elements are adjusted. so that the gain atained thereby is greater than the loss due to the circuits, such disturbance entering the singing path will increase in magnitude and change in frequency until a limit, determined by the energy handling capacity of the elements, is reached, thereby resulting in what is commonly known as singing of the repeaters.

This is objectionable because it impairs the transmission of the repeater circuit, and, therefore makes supervision by the operators over this circuit moredifiicult. This invention provides means to prevent the singing of the repeater during the period preceding the establishment of the through-line connection, and during such times thereafter when any key of a cord circuit, other than the monitoring key has been operated.

Furthermore, when a four-wire circuit of the type heretofore referred to', which is adapted to have a. transmission equivalent better than zero between its terminals, is connected at each end with another trunk line, the transmission equivalent of the complete circuit will depend largely upon the transmission equivalents of the lines connected at each end. Thus, if the repeaters of the four-wire circuit are adjusted so as to give a gain such'that when the fourwire circuit connects the two longest trunk circuits, the transmission over the throughline connection will be satisfactory, it is evident that when the same four-wire circuit connects together two shorter trunk circuits having better transmission equivalents than the trunk circuits previously mentioned a better grade of transmission will be obtained. It is desirable that the transmission over various through-line circuits shall be substantially uniform and it is one of the objects of this invention to provide means to regulate the transmission gain so as to equalize the equivalents of all classes of telephone connections.

Further objects of this invention will appear from the following description of the invention when read in connection with the attached drawing embraced in Figures 1, 2 and 3, which, when Figs. 2 and 3 are respectively placed to the right of the preceding figure, represents a circuit diagram of one embodiment of the invention.

Fig. 1 shows the jacks J and J 2 constitut- 'and L which typify two groups of two-wire trunk lines with which the four-wire circuit is adapted to be connected by means of a toll cord circuit at oflice' X.

Fig. 2 represents a four-wire transmission circuit terminating in one office in jack J and in the other ofiice in jack J and having associated therewith'repeater elements A, and A which are connected with the twowirebranches 1 and 2 respectively.

Fig. 3 which is similar to Fig. 1 represents a toll cord circuit at oflice for connecting the four-wire circuit with the trunk lines extending from that office.

In Fig. 1, L and L represent two telephone trunk lines which terminate at the oflice X in the jacks J and J respectively. L represents a long trunk line over which supervision is maintained by alternating current, on account of its length. L is typical of short-haul trunk lines over which supervision may be maintained by direct current. A toll cord circuit, located at the said ofiice for the purpose of connecting the four-wire transmission circuit with either of the lines L or L terminates in plugs P and P plug P being normally adapted to be inserted in jack J or J and plug P, being normally adapted to be inserted in 'ack J of the four-wire circuit shown in ig. 2 although plug P may be inserted in jack J and plug P in jack J,. The toll cord has associated with it a key K the right hand contacts of which are adapted to establish a monitoring'connection between the operators telephone set and the lines with which the cord circuit may be connected, and the left hand contacts of said key for the purpose of establishing a talking connection. Toward the right hand side of the cord circuit is a ringing key K by means of which ringing current may be applied to lines connected with either end of the cord circuit. A splitting key K is adapted to open the two sides of the cord circuit and thereby separate [the circuits connected with each end of the cord circuit. This cord circuit is adapted for both alternating current and direct current supervision by means of relays R, and R respectively. The other relays shown in connection with this cord circuit provide part of the means for the prevention of singing of the repeaters and for equalizing the transmission equivalents of the through-line connections, and will be more fully described later in connection with the description of the mode of operation of the transmission circuit. v

Fig. 2 represents a four-wire telephone transmission circuit terminating at the ofiice X in the jack J and at the office Y in the jack J... This four-wire circuit is of the usual type, consisting of two two-wire adapted to regulate the transmission equivalent of the four-wire transmission circuit. Connected with'the two-wire terminals in which the four-wire circuit terminates at the offices X and Y are net works 9 and 10, respectively, which are designed to give sufficiently accurate balance to prevent sing ing of the repeater, and at the Same time to permitsatisfactory transmission between operators at the ofiices X and Y, which is necessary for proper supervision. lays shown inthis figure cooperate with those shown in Fig. 1 for the purpose of controlling the selection and the connection of the various networks with the circuit and their function will be more fully described hereafter in connection with the description of the mode of operation of this circuit.

Fig. 3 shows a telephone cord circuit similar to that shown in Fig. 1. This cord circuit terminates in plugs P and P P being normally adapted for connection with pick J' of the four-wire circuit, and plug being normally adapted for connection with jacks J and J of trunk lines L and L which extend from ofiice Y. Lines L and L are of the same type as lines L, and L respectively. shown in Fig. 1, and heretofore referred to. However. plug P may be inserted in jack J of line L and plug P in jack J since the cord circuit is adapted to function properly when so connected.

Let it be assumed that the operator at oflice X has received an incoming call over line L., and it is necessary in order to complete the desired connection. to establish a circuit from line L over the four-wire circuit to the ofiice Y, and thence over trunk line L to the local office in which the line of the desired party terminates. After the operator at X has obtained the requisite information by inserting plug P in jack J and talking with the operator at the distant end of line L. the operator at oflice X i11- serts the plug P in the jack J of the fourwire transmission circuit. By the insertion of plug P in jack J a circuit is established from battery B winding of relays R and R sleeve contacts of plug P and jack J resistance 11 to ground. Since resistance The. re-

11 is sufliciently low, .relays R and R will be operated. By the operation of the lowercontact of relay R, the circuit of the direct current supervisory relay R is opened thereby removing the bridged relay from the line. This is desirable since lines such as L use only alternating current for supervisory signaling. By the operation of the upper contact of relay R3 a ground is removed from conductor 12, the function of which will be shown later. By the closing of the upper contact ofrelay R, the tip side of the cord circuit 1s completely closed through; and by the closing of its lower contact-20 the winding of relay R 18 grounded, closing a circuit from battery 15,, through the winding of relay It, to ground, thereby causing the operation of said relay. w

By the insertion of plug P In jack J a circuit is established from battery B winding of relay R sleeve contacts of plug P and jack J windings of relays R, and R to ground, thereby causing the operation of relays R and R Relay R, is marginal and under the conditions mentioned does not receive sufiicient current to operate it.

eration of relay R and in consequence thereof the lighting of the lamp S which is associated with jack J this signal the operator at Y inserts plug P of her cord circuit in jack J, and-0perates the talking key K, of her cordcircuit so that she may converse with the calling operator. When the left hand contacts of key K of the cord circuit at ofiice X and the right hand contacts of key K, at Y are operated a ground is put upon the windings of relays R and R which causes the operation of the said relays and by the closing of their upper and lower contacts the circuits, which are normally closed through the contacts of said relay, are thereby opened.

- Let us assume that in order to complete the desired connection the operator at Y has inserted plug P in jack J of line L and that the operators at both ofiices have restored to their normal positions all the keys of both cord circuits so that the completed through-line circuit is adapted for' the best talking conditions. When the key K of the cord circuit at X has been restored to its normal position the ground 1s removed from relay R thereby deenergizing this relay. Since relay is operated,

In response to marginal relay R 'is operated. By the closwhich have the same impedance as the lines,

are normally connected into the two-wire terminals of the four-wire circuit they balance the repeater circuit and prevent the singing of the repeaters which otherwise would result from the unbalanced condition of the circuits connected with eac'h end of By the removal of the four-wire circuit. these networks, which act as impedance bridges across the terminals of the four-wire circuit, the transmission over the entire through-line connection is improved thereby and the desired transmission equivalent of the said through-line connection is at-. tained. v

. If it becomes necessary for an operator to talk over the circuit after the throughline connection has been established, it is desirable, in order to prevent singing of the repeaters, to reconnect networks 9 or 10 or both of them during the period in which such supervision is maintained. Thusif the operator at oflice X, for example, desires to maintain such supervision she moves key K to the talking position, thereby grounding "conductor 14 and the winding of-relay R circuit at office Y if the operator at this a four-wire telephone repeater'circuit whenever the desired through-line connection has been completely established and all cord circuit keys, except the monitoring key, restored to their normal positions; and for automatically reconnecting said networks Whenever any. keys, other than the monitor" ing key, have been operated, or Whenever received a call over the line L which has a lower transmission equivalent than lines of the group represented by L,. The operator at X inserts plug P of the cord circuit in jack J and by throwing the key K, to its talking position she learns from the operator at the distant end of the line L that a telephone connection is required which necessitates the use of the four-wire circuit extending to the office Y, and also of the line L extending from the latter office to a distant local ofhce.

The operator at X inserts plug P, of her cord circuit in jack J 3 of the four-wire circuit, and by means of key K she signals to the operator at Y, who responds by inserting plug 1? in ack J and then inserts plug P in jack J of line L,. When the plug P was inserted in jack J 2 a circuit was established from battery 13,, windings of relays R and R sleeve contacts of plug P and jack J and resistance 19 to ground. Relay R will be operated thereby, but on account of the high value of the resistance element 19, the marginal relay R, will not be operated. In consequence of the non-operation of relay R the direct current supervisory relay R remains bridged across the line, which is necessary since L is of that type of lines over which direct current is used for supervisory signalling. Relay R, will be operated through the closing of contact 20 of relay R but in view of the fact that key K is still in its talking position, relay R will be operated which, by the opening of its contacts 15 and 16, opens the circuits through the contacts of relay R and by the opening of contact 17 opens the circuit from relay R to relay R When plug P, has been inserted in jack J relays R and R, will be operated but marginal relay R, will not be operated. After the operator at Y has established the desired through-line connection by inserting plug P in jack J of the line L and the called subscriber has answered, the operators at both oflices restore all the keys to their normal positions, thereby removing the ground from relay R at office X and from the corresponding relay R of the cord circuit at oflice Y and the said relays will be deenergized. Through the deenergization of relay R at oflice X its contacts 15, 16 and 17 are closed. Since relay R, has already been operated, a circuit will be established from battery B contact 26 of relay R contact 16 of relay R con ductor 13, through part of the winding of relay R sleeve contacts of plug 1 and jack J and windings of relays R, and R to ground. Relay R, now receives sufficient current to effect its operation, thereby closing its upper-contact 18 which disconnects the network 9 from the four-wire circuit. Since relay R, has been operated by the insertion of plug P, in jack J a circuit will be established from battery 13,, winding of relay R contact 27 of relay R conductor 22, contact 15 of relay R contact 28 of relay R and cont-act of relay R to ground. It will be recalled that relay R is not oper ated owing to the hi h value of resistance element 19. Relay Ti is operated and closes momentarily a circuit from battery 13,, contact of relay R conductor 29, contact 30 of relay R through the upper wind-' ing of relay R and contact 21 of relay R to ground, thereby causing the operation of relay R which is locked up by current through a circuit from battery B lower winding of relay R contact 31 of said relay and contact 23 of relay R to ground. Through the closing of the upper contact of relay R a circuit is established from ground, conductor 24, to point 25 where the circuit divides, one branch extending through windings of relays R and R and battery B and the other branch through windings of relays R and R and the battery 13,, thereby effecting the operation of all of the said relays. As the result of the operation of relays R and R network 5 is connected into the two-wire branch 1 of the four-wire circuit, and as the result of the operation of relays R and R network 7 is connected into the two-wire branch 2 of the four-wire circuit. ner networks 6 and 8 at office Y will be connected into the two-wire branches, 1 and 2, respectively, of the four-wire circuit, when the plug P of the cord circuit at oflice Y has been connected with the line L which represents a short haul trunk, similar to line L If the operator at ofi'ice X, for example, desires to supervise the completed throughline connection by throwing key K,, to its talking position, the winding of relay R will be grounded thereby, thus causing the operation of the said relay which in turn results in the opening of the contacts 15,- 16 and 17. Through the opening of contact 16, battery 13, is disconnected from the wind ing of relay R and marginal relay R is deenergized thereby. Contact 18 of relay R, is thereby opened which results in the re connection of network 9 with the two-wire terminal of the four-wire circuit, thus preventing the singing of the repeater during the time in which the operator is supervising the connection. As soon as the key K is restored to its normal position, relay R is deenergized, and through the closing of its In a similar man-.

normal contacts, the marginal relay Rais again operated which results in the disconnection of the network 9 thereby restoring the through-line, connection to the position for maximum operating efiiciency.

When the subscribers lines have been disconnected at the distant ends of trunk lines L and L the operators at X and remove the plugs of their cord circuits from the lines L and L and the terminals of the four-wire circuit. When the plug P is disconnected from the jack'J at ofiice X relays R, and R are thereby deenergized, thus allowing their contacts to open which results in the reconnection of network 9 with the two-wire terminal of the four-wire cirwill be seen, therefore, that this invention provides the means for varying the trans.

mission equivalent of the four-wire repeater circuit whereby the transmission -equivalents of all through-line telephone connections which are established over the said four-wire repeater circuit may be made substantially uniform.

Although this invention has been shown as embodied in a particular form, it is evident that it is capable of embodiment in other and different forms without departing from the spirit of the appended claims.

What is claimed is:

1. In a. signalling system the combination of a four-wire transmission circuit having a plurality of telephone repeaters associated therewith, a plurality of trunk circuits, cord circuits adapted to connect each trunk circuit with the said four-wire circuit, a network at each end of said four-wire circuit having electrical characteristics simulating those of said trunk circuits, and a second network arranged to balance the said first network when a trunk circuit is disconnected from the said four-wire circuit.

2. In a signalling systemthe combination of a four-wire transmission circuit having a plurality of telephone repeaters associated therewith, a plurality of trunk circuits, cord circuits adapted to link said trunk circuits with said four-wire circuit, anetwork having electrical characteristics simulating those of said trunk circuits, a second network normally connected with said four-wire circuit adapted to balance the said first network, and means controlled by said cord circuit whereby said second network may be electrically disconnected from said four-wire circuit whenever said trunk is connected with said four-wire circuit and all keys of said cord circuit are in-their normal position.

3. In a signalling system combination, a four-wire transmission circuit having a plurality of repeaters associated therewith a lurality of trunks adapted to be connector wlth said transmission circuit, a plurality of cord circuits adapted to connect said trunk circuits with said transmission circuit, a network at each end of said four-wire circuit adapted to balance said trunks, a second network normally connected with said transmission circuit adapted to balance said first network when said trunk is disconnected from the transmission circuit and 'means associated with said cord circuit said four-wire circuit normally effectively connected thereto adapted to balance said first mentioned network and switching means associated with each second network and controlled by the associated cord circuit whereby said second network may be effectively removed from the four-wire circuit whenever a trunk circuit is connected with the four-wire circuit.

5. In a signalling system the combination of a four-wire transmission circuit having a plurality of repeaters associated therewith, a plurality of trunks adapted to be connected with said four-wire circuit, a plurality of cord circuits adapted to connect said trunks with said four-wire circuit, a network at each end of said four-wire circuit adapted to balance electrically any of saidtrunks, a second network at each end of said fourwire circuit normally eiiectively connected thereto adapted to balance said first mentioned network when the four-wire circuit is disconnected from other circuits, and means to disconnect effectively said second network when a trunk'circuit is connected thereto by means of one of said cord circuits and all keys of said cor'd circuit are in their normal position.

6. In a signalling system the combination of a four-wire transmission circuit having a plurality of repeaters associated therewith, a' plurality of trunks adapted .to be con-1w tively connected thereto adapted to balance with, a plurality of trunks adapted to be said first mentioned network when the said four-wire circuit is connected to one end of said cord circuit and the other end .is disconnected from said trunk, and means to disconnect said second network when atrunk circuit is connected thereto by means of one of said cord circuits and all keys of said cord circuit are in their normal position.

7. In a signalling system the combination of a four-wire transmission circuit having a plurality of repeaters associated thereconnected with said four-wire circuit, a plurality of cord circuits adapted to connect said trunks with said four-wire circuit, a network at each end of said four-wire circuit adapted to balance electrically any of said trunks, a second network at each end of said four-wire circuit normally eifectiv'ely connected thereto adapted to balance said first mentioned network when one of the keys of the said cord circuit has been operated after said four-wire circuit has been connected with one of said trunks, and means to disconnect said second network when said key has been restored toits normal position.

8. In a signalling system the combination of a four-wire transmission circuit having a plurality of repeaters associated there-' with, a pluralityof groups of trunks adapted for connection with said four-wire circuit, cord circuits to effect such connection, a plurality of artificial lines adapted to be connected with each of the two-wire branches of the four-wire circuit, means controlled by the connection of the cord circuit with any trunk of one group whereby said artificial lines may be connected into the four-wire circuits, thereby reducing the transmission gain of the four-wire circuit.

9. In a signalling system the combination of a four-wire transmission circuit having a plurality of repeaters associated therewith, a plurality of groups of trunks adapted for connection with said four-wire circuit, cord circuits to effect such connection, a plurality of artificial lines adapted to be connected with each of the two-wire branches of the four-wire circuit, and means associated with the sleevesof the jacks in which the said trunk circuits terminate, whereby the magnitude of the current for operating the relays associated with said artificial lines may be controlled.

In testimony whereof, I have signed my name to this specification this 7th day of August, 1919. i

CHARLES S. DEMAREST. 

